The bomb exploded as the market in the town of Parachinar was crowded with shoppers buying warm clothes for winter, said Mahtab Hussain, a local government official.

Husain said some of the critically wounded people were airlifted to hospitals in other cities.

All 22 killed were minority Shiite Muslims, said another local government official, Nek Mohammad.

The explosion was caused by a remote-controlled bomb planted in the market, the two officials said.

Parachinar is the main town in the Kurram tribal region, a predominantly Shiite Muslim area which has been troubled by Islamic militant and sectarian violence. Pakistan's military has carried out regular operations in the region to eliminate militants and control sectarian strife.

No one immediately claimed responsibility for the attack. Suspicion would likely fall on al-Qaida and Pakistani Taliban-linked Sunni militant groups, who consider the Shiites to be heretics.

The Taliban and allied Islamic militants have been waging a war against the state for over a decade, killing tens of thousands of people.